1. Field of the Invention
The present invention relates to systems and techniques for determining mask patterns for photolithography processes that use photo-masks and write patterns for maskless-lithography processes that use write devices.
2. Related Art
Lithography processing represents an essential technology for manufacturing Integrated Circuits (IC) and Micro-Electro-Mechanical Systems (MEMS) and Nano-Electro-Mechanical Systems (NEMS). Lithographic techniques are used to define: patterns, geometries, features, shapes, etc. onto an integrated-circuit die, semiconductor wafer, or chips. These patterns are typically defined by: a set of contours, lines, boundaries, edges, curves, etc., which generally surround, enclose, and/or define the boundary of the various regions which constitute the patterns.
One existing lithographic technique is photolithography, in which images defined by photo-masks are printed onto an integrated-circuit die or one or more semiconductor wafers. Furthermore, another existing lithographic technique is maskless lithography, in which a write device directly prints a write pattern onto the integrated-circuit die or the one or more semiconductor wafers, thereby eliminating the need for photo-masks. Unfortunately, it is increasingly difficult to determine the write patterns, or to design and manufacture photo-masks.
In particular, demand for increased density of features on the integrated-circuit die and the one or more semiconductor wafers has resulted in the design of circuits with decreasing minimum dimensions. These trends have significantly increased the complexity of the computations necessary to determine the write patterns and/or the mask patterns (to which the photo-masks correspond), with a commensurate impact on computation time, processing requirements, and expense.
Furthermore, due to the wave nature of light, as dimensions approach sizes comparable to the wavelength of the light used in the photolithography processes, the resulting wafer patterns deviate from the corresponding photo-mask patterns and are accompanied by unwanted distortions and artifacts. Existing techniques (such as Optical Proximity Correction or OPC, and resolution enhancement technologies or RET) are used to pre-distort the mask patterns to improve resolution and/or a process window (e.g., a range of process conditions that result in acceptable yield) in a photolithography process. While these techniques may ensure that the wafer pattern is printed more accurately, determining the pre-distorted mask patterns is increasingly difficult, thereby exacerbating the computational complexity and the associated problems.
Additional techniques to increase the resolution (or decrease the critical dimension) for a given wavelength of light and/or to improve process control include multiple-exposure lithography. For example, a wafer pattern may be printed by sequentially exposing and/or patterning a wafer using photo-masks (which correspond to mask patterns) that represent a decomposition of a photo-mask used in a corresponding single-exposure photolithographic process. Unfortunately, it is very difficult to perform this decomposition for an arbitrary mask pattern or write pattern.
Hence, what is needed is a method and an apparatus that facilitates determination of write patterns and mask patterns without the above-described problems.